A plasticizer is a material incorporated in a plastic to increase the workability, flexibility on distensibility (elongation) of the plastic. Plasticization or the molecular level, according to theory, is the weakening or rupturing of selective "bonds" while leaving others strong to make possible the shaping, flexing or molding of the material being plasticized.
Although natural plasticizers, e.g., water, camphor, oils, pitch, etc., have been used since the earliest days of recorded history, it has only been since the early 1900's that synthetic materials have been used to plasticize resins and polymers. Since the advent of polyvinyl chloride (PVC), the most generally used synthetic plasticizers have been the esters of phthalic and phosphorus acids, e.g., dioctyl phthalate, diphenyl phthalate, tricresyl phthalate, triphenyl phosphate and the like. Monomeric plasticizers, while admirably fulfilling their function of external plasticization of PVC, have lately come under increasing pressure from environmentalists since they are known to "bloom", i.e., exude to the surface of a plasticized polymer and migrate to other materials in contact therewith. Despite the regulatory status and long safe history of plasticizer usage, the migration of phthalates and other plasticizers to medical and food products has caused considerable concern and incentive to search for truly permanent external plasticizer systems.
Because of the shortcomings of conventional monomeric plasticizers, e.g., volatility, extractability and migration, a considerable amount of research has been conducted in an effort to develop a truly permanent, high molecular weight polymeric modifier for PVC which is nonfugitive. The term "plastifier" has been coined to describe such modifiers to distinguish them from the conventional liquid to semi-solid type external plasticizers, usually monomeric, heretofore used as modifiers for PVC. The need is obvious for a plastifier which would have the properties of high permanence in the plastified system and good efficiency combined with a low order of toxicity and environmental safety.
1. Summary of the Invention
It has now been found that copolyesters and copolyesterurethanes, having a particular structural sequence of amorphous and semi-crystalline blocks and which are of a high molecular weight, may be used as plastifiers for PVC. Such plastifiers afford a high degree of permanence with good efficiency, low toxicity and environmental stability. As will be further described hereinafter, the plastifiers of this invention may be prepared in random or ordered fashion to afford block copolyesters and block copolyesterurethanes useful as plastifiers for PVC.
2. Prior Art
Following is a description of the most pertinent prior art known to applicant:
U.S. Pat. No. 2,691,006 describes linear ordered crystalline copolyesters containing a plurality of polyester sequences, at least two of which have an average sequence length of at least two ester units. The copolyesters are prepared by coupling separately prepared different polyesters. Thus, a hydroxy-terminated polyester and an acid chloride-terminated polyester are condensed or two separately prepared polyesters having both hydroxy and carboxyl end groups may be coupled with a diisocyanate or other coupling agent. In the preparation of the polyesters, which may be coupled or condensed with each other, there are used aromatic or aliphatic dicarboxylic acids and glycols. There is no concept disclosed which describes the combining of amorphous and crystalline polyesters to obtain a high molecular weight copolyester having particular sequences of amorphous and crystalline structure.
U.S. Pat. No. 3,446,778 describes the preparation of composite copolymers characterized by a crystallizable predominantly aromatic polyester block and an amorphous rubbery block. The crystalline and amorphous blocks are joined via a coupling agent. There is no concept of sequentially coupling a polyester prepared from a diacid and a non-crystallizing glycol with a polyester prepared from a diacid and a mixture of crystallizing and non-crystallizing glycols.